1. Field of the Invention
The present invention relates to a surface wave dispersive filter spectrum analyzer.
Real time spectrum analyzers have undergone considerable development during these latter years among which we find entirely digital systems, or systems using analog techniques, such as surface wave dispersive filter analyzers to which the present invention relates. These latter use for example a so called "M-C-M" (multiplication-convolution-multiplication) structure, by means of which the spectrum of a signal to be analyzed is obtained by premultiplying the signal by a first linearly frequency-modulated ramp R.sub.1 (t) of band B and duration T, then effecting the convolution of a signal thus obtained with the second linearly frequency-modulated ramp R(t) of band 2B and duration 2T, and of a slope opposite R.sub.1 (t), and by postmultiplying the signals thus obtained by a third linearly frequency-modulated ramp R(t), of band B and duration T, and of a slope identical to R.sub.1 (t).
These frequency ramps are advantageously obtained from the pulse response of surface wave dispersive filters.
Thus, the premultiplication ramp R.sub.1 (t) is obtained by driving a first dispersive filter, called premultiplication filter, by a Dirac pulse .delta..sub.1 (t). Similarly, the post multiplication ramp R.sub.2 (t) is obtained by driving a second dispersive filter, called postmultiplication filter, by a Dirac pulse .delta..sub.2 (t) which is initiated with a delay T with respect to pulse .delta..sub.1 (t). Finally, the convolution with ramp R(t) is obtained by passing through a dispersive filter, called convolution filter, having a pulse response R(t).